Method of geophysical prospecting of ore deposits

ABSTRACT

A geophysical method of prospecting for ore deposits which serves to determine the mineral composition, position and size of ore bodies in situ, as well as to correlate the intersections of the ore body by different boreholes and mine workings. The method is based on the selective excitation and registration of electrochemical reactions of certain minerals contained in the ore bodies. The successive excitation and registration of the electrochemical reactions is achieved by gradually varying the intensity of the current passed through an ore body, by simultaneously registering in the form of polarization curves the current intensity and the ore body potential relative to the enclosing rocks taking into account a drop of voltage in said rocks and by determining from said curves the potential values and the limit current intensity of the electrochemical reactions on the basis of which the mineral composition, position and size of the ore body are established.

United States Patent 1191 1111 3,758,846

Ryss et a1. 1 Sept. 111, 1973 METHOD OF GEOPHYSICAL 2,250,024 7 1941 Jakosky 324 1 PROSPECTING 0 ORE DEPOSITS 3,113,265 12/1963 Woods et a1 324/1 [76] Inventors: Jury Samuilovich Ryss, 2 Murinsky pr., 14, kv. 39; Tamara Mikhailovna Ovchinnikova, ul. Detskaya, 26, kv. 31; Jury Georgievich Gavrilov, Morskoi pr., 25, kv. 114; Dmitry [57] ABSTRACT Vyacheslavovich Voronin, 12 Linia, l7, kv. 1; Vladimir Mikhailovich Primary Examiner-Gerard R. Strecker Attorney-Waters, Roditi, Schwartz & Nissen A geophysical method of prospecting for ore deposits which serves to determine the mineral composition, po- Pantelelmonof Nevsky 1 sition and size of ore bodies in situ, as well as to correof Lemngrad late the intersections of the ore body by different bore- 22 i May 6 1971 holes and mine workings. The method is based on the selective excitation and registration of electrochemical [2]] Appl' 140,868 reactions of certain minerals contained in the ore bod- Rehed Application m ies. The successive excitation and registration of the l 63] continuatiomimpan of Ser No. 56,097 June 30 electrochemical reactions is achieved by gradually 1970, abandoned, which is a continuation of Ser. No. varymg the mtens'ty of the current passed through an 643285 June 23 1967 abandoned' ore body, by simultaneously registering in the form of polarization curves the current intensity and the ore 521 u.s. c1. 324/1 y potential relative to the enclosing rocks taking 51 Int. Cl GOlv 3/02 into account a p of voltage in Said rocks and y [58] Field of Search 324/1, 9, 10 termining from Said Curves the Potential Values and the limit current intensity of the electrochemical reactions 5 References Cited on the basis of which the mineral composition, position UNITED STATES PATENTS and size of the ore body are established.

2,190,322 2/1940 Potapenko 324/1 2 Claims, 10 Drawing Figures 9 1 /7 Y4 I l PATENTEUSEH 1 I918 3.758.846

SHEET 3 OF 3 2 5 456mm r FIG. ll]

METHOD OF GEOPHYSICAL PROSPECTING OF ORE DEPOSITS This application is a continuation-in-part of our earlier filed copending application, Ser. No. 56,097, filed June 30, 1970 (now abandoned) which is a continuation of application, Ser. No. 648,285, filed June 23,

1967, now abandoned.

The present invention relates to the prospecting and exploring ore deposits and, more particularly to methods for the geophysical prospecting of ore deposits, which serve to determine the mineral composition, location and size of ore bodies in situ.

At present the mineral composition and the size of ore bodies can be determined by geological methods.

To this end, areas to be explored are covered by a network of bore-holes and test cores are extracted. The latter are subjected to visual, microscopic, chemical and other analyses.

One of the essential disadvantages of these methods is that the non-homogeneous and intricate distribution of useful components in the ore body necessitates a large-scale program of laborious and expensive boring, as the comprehensiveness of the characteristics of the mineral composition of the ore body depends upon the number and positioning of bore-holes intersecting the ore.

It is an object of the present invention to provide a method and apparatus for geophysical prospecting of ore deposits which would permit determining the mineral composition, size and location of ore bodies in situ without intersecting the ores by means of bore-hole, working, pits or the like, or with crossing them but once at any point in the ore body without extracting a test core.

The method is based on the known phenomenon of excitation of individual electrochemical reactions on the interface of media with electronic conductivity (ore body) and ionic conductivity (enclosing rocks) when passing an electric current therethrough.

What reactions will develop on the interface of the two media having different types of conductivity depends upon their constituent composition.

According tothis and other objects and proposed method of geophysical prospecting of ore deposits consists of passing an electric current of gradually varying intensity through an ore body, thereby exciting electrochemical reactions following one after another on the boundary of said ore body with the enclosing rocks, then registering the potentials of these reactions for each current intensity value and plotting so-called electrochemical curves on the bases of the measured current intensity and potential values, said curves being helpful for establishing'the mineral composition, location and size of the ore body.

According to the first embodiment of the invention, by directly connecting the source of exciting current to the point ofthe intersection of the ore body by a mining or a bore-hole either cathode or anode electrochemical reactions, depending on the polarity of the applied exciting electric current, may be excited throughout the entire boundary of the ore body with the enclosing rocks. 4

In accordance with the second embodiment of the invention, an electric current is passed through an ore body without direct contact of the ore body with the source of exciting current and thereby cathode reactions are excited in one sector of the are body boundary with the enclosing rocks and simultaneously anode reactions are produced in the other sector of the boundary and then at the opposite polarity anode reactions are excited in the first sector and cathode reactions in the second sector.

The successive excitation of electrochemical reactions at the boundary of the ore body with the enclosing rocks may be achieved by a gradual increase of the current intensity from zero to hundreds of amperes at one and the other polarity of the current. A reverse sequence of excitation is possible when the current is decreased from hundreds of amperes to zero at one and the opposite current polarity.

The passing of an electric current at a frequency of less than 20 cps also leads to the excitation of anode or cathode electrochemical reactions depending on the polarity of the flowing current, said reactions succeeding one another as the intensity of the current is gradually varied.

Other objects and advantages of the present invention will be disclosed here-in-below when considering its exemplary embodiments and the attached drawing in which.

FIG. 1 is a schematic electric diagram of a first version of the proposed apparatus;

FIG. 2 is a schematic electric diagram of a second version of the proposed apparatus;

FIG. 3 is an electrochemical curve obtained by means of the apparatus shown in FIG. 1;

FIG. 4 represents electrochemical curves obtained by means of the apparatus shown in FIG. 2;

FIG. 5shows electrochemical curves obtained with the first embodiment of the invention (anode electrochemical curves);

FIG. 6 shows electrochemical curves obtained with the first embodiment of the invention (cathode electrochemical curves);

FIG. 7 shows the summed cathode-anode electrochemical curves obtained in the second embodiment of the invention;

FIG. 8 shows the layout of the sphere and of the points of observation of electrochemical curves shown in FIG. 4; I

FIG. 9 shows the summed cathode-anode electrochemical curves at one of the observation points shown in FIG. 8 and FIG. 10 shows the curves of the dependence of the summed anode-cathode electrochemical reaction potentials, obtained in the second embodiment of the in vention, upon the distance from the observation points to the center of the sphere.

The method of the first embodiment of the invention consist of passing a direct electric current of gradually varying intensity through an ore body, which current causes successive anode electrochemical reactions on the boundary of the ore body with the enclosing rocks at one current polarity while, at the opposite current polarity, it causes successive cathode electrochemical reactions.

Moreover, the succession of the excitation of the reactions may be reversed. By gradually increasing the current intensity from zero to hundreds of amperes, it is possible to excite one reaction after another in the different minerals forming the ore bodies to be examined.

In FIG. 1 the apparatus includes a power source 1, a device 2 for a programmed current change, a current intensity detector 5, a measuring recording device 8, a compensating voltage generator 9, and a summing unit 10.

The apparatus of FIG. 2 includes a power source 1, a device 2 for a programmed current change, a current intensity detector 5, a measuring-recording unit 8, a compensating voltage generator 9, a summing unit 10, and a calculating amplifier 14.

The process of each reaction is characterized by a rigorously definite potential of the ore body at its boundary with the enclosing rocks, which does not vary during the process of reaction with the change of current intensity, and by a limit current intensity of the reaction. The limit current intensity depends upon the area occupied by a given mineral on the ore body surface. The limit current intensity is the strength of the current at which the limit speed of the reaction is attained and the next electrochemical reaction begins.

The process of a reaction is marked on the electrochemical curve of the dependence of the reaction potential upon the intensity of the exciting current by a step consisting of two sections, one of which is parallel to the current axis, while the other to the axis of potentials. The magnitude of the reaction potential is defined as that value of the electrochemical potential starting from which the intensity of the current abruptly changes while the potential at the boundary of the object with electronic conductivity (ore body) and the medium with ionic conductivity (enclosing rocks) remains unchanged.

The magnitude of the limit current intensity is defined as the difference between those values of the exciting current intensity at which the given electrochemical reaction starts and attains its limit speed.

The potentials of the reactions are compared with the established electrochemical reaction potential values. for different minerals as cited in Table 1. (Rd collection of articles Metodika i tekhnika razvedki, No. 65, I969).

the size of the surface and the composition of ore bodies, which are established a result of measurements taken in different bore-holes or workings indicate that the ore intersections belong to different ore bodies.

The potentials of the reactions and their limit currents are determined from the electrochemical curves obtained by registering the value of the ore body potential relative to the enclosing rocks simultaneously with the value of the intensity of the exciting current.

From the registered potential representing the sum of the electrochemical potential on the boundary of the ore body with the enclosing rocks and the ohmic drop of potential on the same section of the exciting current flow path incorporating the enclosing rocks where the potential is registered, it is possible to discriminate the electrochemical potential values.

To this end, from the value of the potential measured for each value of the exciting current, a value proportional to the respective value of current intensity is subtracted. A proportionality factor is selected for each cycle of the current passed, which is taken equal to the smallest value of the rating' of the registered potential increment to the increment of the exciting current causing this potential increment.

Two series of electrochemical curves, namely, anode and cathode series of curves are plotted.

The anode series comes as a result of the examination of the anode reactions on the boundary of the ore body, which are excited through connection of said ore body to the positive pole of the current source, while the cathode series comes a result of a similar examination of the cathode reactions excited through connection of said ore body to the negative pole of the current source. Depending on the complexity of the mineral composition of ores, several electrochemical curves are drawn in either series with varying speeds of the change of current intensity. Owing to both series of curves, it is possible to determine more accurately'the mineral composition and the size of the ore body.

TABLE 1.-ELEcTRo0HEi 1ioxL ItEACIION POTENTIALS Foa n PRINCIPAL MINE RALS Anode processes Cathode processes Potential of Potential of Potential of Potential of 1st process, 2nd process. 1st process, 2nd process, Mineral V V V V Number:

1 Magnetite +1. 605:0. 10 1.45=!=0. 10 2 Pyrrhotite +0. x0. 05 +0. 903:0. 05 0. 503:0. 05 1.50:l:0. 10 Pyrrhite +0. 603:0. 05 0. 50i0.05 3 1.30=i=0. 05 Chalcopyritefiu +0.20=l=0. 10 +0. 75;:0. 10 0 601:0.10 1.40=|=O. 10 6 Chalcozine +0.20=l:0. 10 0 6010.05 -1. 00:1:0. 05 Sphaleritc +0. 15110.05 +2. 30:1:0. 10 1 20:b0.05 2.20:l;0. 10 +0. 305:0. 10 +1. ;l:0. 10 0 :1:0. 1O -1. 50zl=0. 10

0. 4010. 05 +0.80;t=0.05 10 Graphite +1. 50510.05

1 Sometimes 0.70. 1 Sometimes +0.90+1.20. Sometimes -1.80.

The above mentioned object is attained by providing an apparatus for geophysical prospecting of ore deposits which comprises a power supply source with current-carrying electrodes, forming a power supply circuit, and a measuring-and-registering unit with potential nonpolarizable electrodes, constituting a measuring The total sum of the limit currents for all the minerals 65 circuit.

is proportional to the surface of the entire ore body. The size of said ore body surface may be easily calculated by using a proportionality factor. Differences in The power supply circuit comprises a means for a programmed change of the intensity of the current from zero to hundreds of amperes depending on the power of the supply source, which current causes successive excitation of electrochemical reactions on the surface of the ore body.

The power supply circuit also comprises an exciting current intensity detector.

A compensating unit for compensating an ohmic drop of potential in the enclosing rocks is inserted in the measuring circuit between the potential-receiving electrodes and registering unit. The compensating unit for compensating an ohmic drop of potential in the enclosing rocks is inserted between the potentialreceiving electrodes and registering unit.

The compensating unit comprises a summing device in which the compensating voltage proportional to the intensity of exciting current is subtracted from the values of the potential measured by potential-receiving electrodes.

The compensating voltage is produced by a compensating voltage generator connected to the exciting current intensity detector.

It is the values only of the electrochemical potential at the boundary of the ore body with the enclosing rocks that are applied from the summing unit to the registering unit.

The first embodiment of the invention is intended for geophysical prostecting of ore deposits when the ore body 7 has a limited access, for instance when only one bore-hole is drilled, through which a current-carrying electrode 3' is directly lowered into the ore body as is shown in FIG. 1.

In the second embodiment of the invention, the apparatus is intended for geophysical prospecting when the ore body 7 is completely inaccessible as shown in FIG. 2.

In accordance with the invention, the apparatus comprises a power supply source 1 with a device 2 for a programmed change of the current intensity in the power supply circuit, which current causes successive, with respect to time, excitation of electrochemical reactions on the boundary of the ore body with the enclosing rocks, current-carrying electrodes 3 and 4, a current intensity detector 5, connected in series with the power supply source 1 and the electrodes 3 and 4, which together with the enclosing rocks 6 and the ore body 7 under study form a power supply circuit.

The current intensity detector 5 is connected to a measuring and registering unit 8 and a voltage compensating generator 9, the latter in its turn being connected to the summing device 10, which unit is connected with nonpolarizable potential electrodes 11 and 12 and with the measuring-and-registering unit 8.

The power supplysource 1 with the means 2 constitutes a rectifier provided with a regulator, whose output voltage is automatically changed under a prescribed program so that the current flowing in the power supply circuit is changed according to the same program. The current-carrying electrode 3-4 provide for the flow of the current through a closed circuit from the current supply source 1 via the enclosing rocks 6 and ore body 7.

In the first and second versions of the apparatus, the current intensity detector 5 is a precision fixed resistor 5 (FIGS. 1,2), capable of dissipating high power without any change of its parameters.

The measuring and registering system of unit 8 is calibrated along the axis of ordinates for measuring the intensity of the current in the power supply circuit, while along the axis of the abscissae this system is calibrated for measuring the voltage. The input Y of unit 8 is connected to the resistance 5', while the input X is connected to the output of unit 10.

The summing unit 10 comprises a calculating amplifier 14 with a feedback resistor 15 and summing resistors l6 and 17.

In the first version of the proposed apparatus, the compensating voltage generator 9 is merely a variable resistor 18 (FIG. 1) provided for changing the value of the output voltage of this generator.

In the second version of the proposed apparatus, the compensating voltage generator 9 includes a variable resistor 18 (FIG. 2) for selecting the value of the output voltage of generator 9 (or for changing its amplification factor), a switch 19 for changing the polarity of the ouput voltage, capacitors 20 and 21 and a commutating relay whose contacts 22-23 provide for transmission of the compensating voltage from the variable resistor 18 to the capacitor 21 without galvanic coupling between these elements.

The principle of operation of the proposed apparatus consists of the following.

Electrochemical reactions are excited in succession on the boundary of the ore body with the enclosing rocks when an electric current is passed therethrough subsequent to the change of the exciting current according to a prescribed law.

The nonpolarizable potential electrodes take the difference of the electric potentials at the corresponding points of the enclosing rock. The measured potential difference may vary when working with real ore objects from a few volts to a hundred volts. The potential difference comprises a voltage bearing useful information about the character of the electrochemical reactions and the interference voltage, the latter being equal to the ohmic drop of potential on the ore body and in the enclosing rocks. The magnitude of the interference voltage is often from two to three orders higher than the magnitude of the voltage bearing useful information about the electrochemical reactions, the value of the reactions being often not higher than dozens of microvolts.

The voltage bearing the information about the electrochemical reactions is recorded in the form of graphs (electrochemical curves) in the measuring-andrecording unit so that each value of the current corresponds to the value of the potential of the electrochemical reaction at the same moment.

A voltage proportional to the potential of the electrochemical reaction and applied to the measuring-andrecording unit is developed at the output of the summing unit whose input is fed with voltage from the nonpolarizable potential electrodes and from the compensating voltage generator.

The compensating voltage generator produces a voltage changing according to the same law by which the current flowing through the ore body is changed. The value of the compensating voltage is equal to the interference voltage between the nonpolarizable potential electrodes but of the opposite polarity. Thus the recording of the electrochemical curves makes it possible to draw certain conclusions about the mineral composition, location and dimensions of the ore body.

Described below are concrete examples of operation of different versions of the proposed apparatus. The apparatus in the form of the first version (FIG. 1) operates as follows.

On passing a direct current of varying intensity through the circuit: power source 1, resistor 5, current-carrying electrode 3, enclosing rocks 6 together with the ore body 7, current-carrying electrode 4 and means 2 for a programmed change of the current intensity, a portion of the total current will flow through the ore body 7 to be prospected, which will excite electrochemical reactions on the surface of the ore body 7, each such reaction being characterized by its potential and current arising between the non-polarizing electrodes 11 and 12. By introducing into the voltage being measured the compensating voltage from the generator 9 for taking into account the interference when the current passes through the enclosing rocks 6, at the output of the summing unit 10 the value of the potentials is obtained, these potentials characterizing the electrochemical process taking place at the boundary between the ore body 7 and the enclosing rocks 6. By registering with the help of the measuring-and-recording system of the unit 8, the values of the current and the potentials in the form of a graph =f (I), as shown in FIG. 3, in which the values of the potentials (da) are plotted along the axis of the abscissae, while the values of the current intensity (I) are plotted along the axis of ordinates, a polarization curve 24 will be obtained which is used for the determination of the mineral composition and dimensions of the body 7 being studied.

With the help of the compensating voltage generator 9, the interference is taken into account in the following manner. From the non-polarizing electrodes 11 and 12 to the input of the summing unit 10, there is applied the sum of two voltages U U 1b where U is the interference voltage proportional to the intensity of the flowing current, and d) is the difference of potentials proportional to the potentials of the reactions.

During the change of the current from zero to a certain value and at the zero compensating voltage which is set by adjusting the generator 9, an electrochemical curve is recorded in the measuring-and-recording unit 8. (FIG. 4) This curve is strongly extended along the axis of obscissae and is inconvenient for decoding. It is necessary to record the electrochemical curve with a minimum of distortions caused by the interference voltage U,. For this purpose, the variable resistor 18 is used for setting a definite value of the output voltage of the generator 9, while the switch 19 is employed for setting the polarity of the output voltage, which through capacitor 20 and vibrating contacts 22 and 23 of the relay is applied to capacitor 21 serving as an output element of the compensating voltage generator 9.

The summing unit 10 is fed with voltage U from the nonpolarizable potential electrodes 11 and 12 through the summing resistor 17 and with the compensating voltage U from the output of the generator 9 through the summing resistor 16.

In the process of changing the current in the power supply circuit, a voltage is developed at the output of the summing unit 10, which voltage is equal to the algebraic sum of the interference voltage U,, compensating voltage U, whose polarity is opposite to that of the interference voltage, and the potential difference (1), proportional to the potentials of the electrochemical reactions. The resultant of the algebraic summation of these voltages is applied from the output of the unit 10 to input X of the measuring-and-recording unit 8, the

input Y of the unit 8 being simultaneously fed with the voltage from resistor 5 for registering the intensity of the following current.

If the output compensating voltage U of the generator is less than the interference voltage U,, the electrochemical curve 26 is recorded in the measuring-andrecording unit 8. If U U,, the curve 27 is recorded. When operating the proposed apparatus it is desirable to obtain the curve 28 recorded under the condition U U2.

In FIG. 4 for plotting the curves 25, 26, 27 and 28, the values of the algebraic sum of the interference voltage, compensating voltage and potential (4)) proportional to the values of the reaction potentials are plotted against the axis of abscissae in FIG. 4, while the values of the current intensity (I) are plotted against the axis of ordinates.

When arranging the current-carrying electrodes 3 and 4 on the earth surface at a certain distance from the electrodes 11 and 12, a current may appear between the electrodes 1 1 and 12 due to the energy of the power source 1, which current will be much higher than the permissible one, and the electrodes may become damaged. To keep the non-polarizing electrodes in good condition, the compensating voltage generator 9 is provided with a dc decoupling circuit inserted between the input and output of the generator, said input being fed by the voltage from the resistor 5' inserted into the power supply circuit.

In the proposed version of the compensating voltage generator 9, the galvanic decoupling is effected by means of the capacitor 20 which through the relay contacts 22 and 23 is alternately connected either to the variable resistor 18 via the switch 19 and is charged, or to the capacitor 21 and is partially discharged therethrough. This process runs until the voltage of the capacitor 21 becomes equal to the compensating voltage U, taken from the variable resistor 18.

The apparatus according to the first embodiment of the present invention (FIG. 1) operates as follows:

By means of electrode 3', an electric current is passed through the ore body 7 so that the current intensity consequitively varies and electrochemical reactions are excited on the surface of said ore body 7. Between the electrode 3 in the ore body 7 and the nonpolarizable electrode 11, with taking into account the compensation of the interference voltage by the compensating voltage generator 9, the algebraic sum of the voltages is measured, which in this case is equal directly to the potentials of the reactions taking place on the boundary of the orebody 7 and the enclosing rocks 6.

By the apparatus of the present invention, the values of the current intensity and potentials are recorded as electrochemical curves, which curves serve for establishing the mineral composition and size of the ore, body.

Inasmuch as one of the current electrodes and one of the potential nonpolarizable electrodes are combined into a single current-carrying electrode 3 located as described above, inside the ore body 7 under investigation, neither galvanic decoupling of the input and output of the compensating voltage generator. 9, nor change in the polarity of the output voltage are required.

The sequence of recording electrochemical reactions and the interaction of the individual units of the apparatus remains unchanged.

In this case the shape of the electrochemical curves does not depend on the position of the non-polarizable potential electrode and due to this fact the processing of the obtained data becomes simpler and quicker. Shown in FIG. 3 is the electrochemical curve 24 obtained by means of the present apparatus, which is used for determining the mineral composition and dimensions of the ore body 7 being prospected.

The proposed apparatus makes it possible within a comparatively short time and either without drilling operations or with such operations quite limited to determine the mineral composition of the ore body, its dimensions and location. The prospecting of the ore bodies with the help of the present apparatus makes it possible to reduce the scope of the drilling operations by a factor of 1.5-2, and improve the quality of prospectmg.

FIGS. 5 and 6 show the electrochemical curves obtained by the method of the first exemplary embodiment.

The electrochemical curves 29 and 30 (FIG. 5) are anode electrochemical curves, while curves 29 and 30' (FIG. 6) are cathode curves. They represent a graphic dependence between the force |.(as measured in ma) and the potential (v) developing on the boundary of the ore body with the enclosing rocks.

The straight lines (shown as dashed in the drawings) continued from the rectilinear portions of the electrochemical curves cut off the values of the potentials of reactions (anode reactions) and (cathode reactions) on the axis of the potentials.

The straight lines 29 and 29' reflect the anode and. cathode processes developing in chalcozine (chalcozine gaug) with the reaction potentials (+0.3)(+0.4) and (+0.2) (+0.l) V, typical of chalcozine.

The curves 30 and 30' are drawn on the basis of a chalcozine-pyrate gaug which is up to m long, said curves being stepwize. Each step of the curve corresponds to a certain electrochemical reaction which is characterized by its value of the reaction potential or Established for anode reactions are potentials +1 +0.35v; +2 +0.52 V and +3 +0.8l V. The value +l +0.35V corresponds according to the tabular data, to the reaction in chalcozine. +2 +0.52 V and +3 +0.81V conform to the reactions in pyrite. For the cathode reactions the potentials obtained are l +0.16V; 2 0.53V -L9V.

According to the tabular data, the reaction potential l +0.16V corresponds in the examined gaug to chalcozine while the potentials =-O.53V and 3 l.9V to pyrite.

The total sum of the limit currents in chalcozine and pyrite amounts to I ma (shown in dashed lines in the drawing) for the cathode reactions. Considering the proportionality factor between the limit currents of the first reactions in cathode processes and the size of the surface of the propogation of reactions for the examined physical-chemical conditions, the total surface of the gaug is 140 m In accordance with this the linear dimensions of said gaug are 8 X 8 or 8 X 9 m, which is in good compliance with the true dimensions of the gaug. Other examples of the application in practice of the proposed method for exploration and prospecting of polymetallic ores may be found in the collection of articles Metodika i Tekhnika Razvedki, No. 65, I969.

The method of the second exemplary embodiment consists in passing an electric current through the ore body without any direct contact of the source of the exciting current with the ore body.

At one direction of the current cathode electrochemical reactions are excited in one sector of the ore body while in the other sector, anode electrochemical reactions are excited.

At the opposite direction of the current in the sectors where cathode reactions took place, anode reactions are excited and, in the sectors where there were anode reactions, cathode reactions are excited. At either direction of the current, its intensity is gradually increased adding successively one by one other reactions to those already developing. For each current intensity value as was previously described with reference to the first embodiment of the invention, the potential is measured in different points of the ore body periphery, taking into account the drop of potential in the enclosing. rocks (the so called apparent potential).

The measured potential depends upon the potentials on the ore body boundary, which are established in different points of the ore body in accordance with the developing cathode and anode reactions, as well as upon the distance from the ore body to the observation point and upon 'the shape of the ore body. For each current intensity value it is also possible to measure the potential gradient.

Stemming from the value of the current strength and the measured potential for each point in the enclosing rocks electrochemical curves are plotted, which reflect the cathode and anode reactions developing on the boundary of the body and which are summed cathodeanode electrochemical curves. By comparing said curves for each point of observation at a straight and reversed directions of the feeding current, it is possible to discriminate cathode from anode curves pertaining to the same sector of the ore body boundary. The separate cathode and anode curves help to determine the apparent reaction potentials do which as has been pointed out, depend upon the distance from the ore body to the observation point and upon the shape of the ore body. By making use of established relationship relating the distribution of the potential in the periphery of the ore body upon its shape and upon the values of the potential on its boundary, it is possible to determine the reaction potentials on the ore body boundary or the so called true reaction potential, and also the location and shape (size) of the examined ore body taking advantage of the value of the apparent potentials.

The mineral composition of the ore body is established through a procedure similar to that used in the first exemplary embodiment, i.e. by utilizing the true reaction potentials and comparing them with tabular values.

From the separate cathode and anode electrochemical curves, the limit currents for each reaction are determined, which are helpful, as in the first embodiment, for establishing the ratio of the ore body minerals with regard to one another and also the size of the ore body surface or the size of its different parts.

FIG. 7 shows the summed cathode-anode electrochemical curves 31, 32, 33, 34 and 35 obtained with the aid of the proposed exemplary embodiment (indicated on the axes are the same values as in FIGS. and 6).

The curves pertain to a copper sphere contained in a solution of 0.004 N NaSO, 0.002 NNaCl 0.002 N CaCl 0.0015 N MgCO plus some CuSO The sphere is placed in a homogeneous electric field of the current. The curves 31, 32, 33, 34 and 35 are measured in different points 31', 32', 33', 34' and 35' of the periphery of the sphere from the side where cathode reactions develope. The positioning of the points near the sphere is shown in FIG. 8. The curves 36 and 37 shown in FIG. 9 are drawn in point 33, the curve 36 pertaining to the case when on the nearest surface of the sphere cathode electrochemical reactions are excited and the curve 37 pertaining to the case when on this surface anode electrochemical reactions are excited.

It is possible to conclude from the examined summed cathode-anode electrochemical curves (FIG. 7) that three reactions are developing in the object under consideration, namely: one cathode and one anode reaction with currents up to 90 ma and plus one more either cathode or anode reaction with current higher than 90 ma. Comparison of the electrochemical curves in one and the same observation point (FIG. 9) at one and the opposite polarity of the exciting current flowing through the nearest portion of the object's surface shows that the added reaction is a cathode reaction, as in the case of cathode reactions its intensity increases while in the case of anode reactions its intensity decreases. From this it follows that two cathode and one anode reactions are developing in the examined object, the anode reaction being characterized by a small potential value. Thus the summed electrochemical curves, in the case of cathode reactions on the surface of the object, almost coincide with separate cathode curves, differing from the latter by an addition at the expense of one anode process.

Calculation of the apparent potentials of the initial cathode and anode reactions for isometric bodies is made in a crude way, namely: a fraction of the potential displacement along the axis of potentials is calculated for the anode reaction in the case of exitation of a cathode process on the nearest portion of the objects surface. From experience, this fraction is about one quarter of the summed displacement of the potential for both reactions.

The value obtained is subtracted from all the values of the apparent potentials of the summed electrochemical curve measured in the case of cathode reactions in the nearest portion of the surface of the object.

From the curves thus obtained, the values of the apparent reaction potentials d), for each observation point are determined considering that the initial potential of the examined object is close to zero.

In the given exemplary embodiment the distances r (FIG. 8) from the center of the object to the curve measurement points were assumed preset. These dis-- tances are generally known to be easily determined during observations on profiles available near the object. The calculated 1) values for all the three reactions are plotted on a bilogarithmic sheet (FIG. on which the values of r (cm) are indicated along the X-axis and the values of 4), (v) along the Y-axis. The curve 38 serves to express the dependence of (1), upon r for the first cathode reaction, the curve 39 likewise for the second cathode reaction and the curve 40 expresses the same dependence for the anodereaction. The obtained curves 38, 39 and 40 have a shape typical of the sphere, with a convexity at small values of r facing the right top corner of the sheet and with a nearly linear portion of the curve for large values of r, the tangent of whose angle of inclination being close to 2. Judging by the shape of these curves it is clear that the examined object is a sphere. By applying a master curve calculated for the sphere to the obtained curves, the radius and true values of the reaction potentials (b, are calculated in a point where its single lines intercross on the sheet grid. In the given instance they are:

Sphere radius Measured value True value l.32-l.4 cm 1.5 cm

lI cathode 4)-;

I anode dz, +0.076 v +0.lv

The measured values of the potentials qS, coincide with the potentials of the electrochemical reactions developing in copper Thus the proposed method permits to determine the composition, location and size of the ore body in situ.

Although the present invention has been described with reference to an exemplary embodiment thereof, various alterations and modifications can be made without departing from the spirit and scope of the invention as those skilled in the art may easily understand.

These alterations and modifications are to be considered as falling within the essence and scope of the invention, as specified in the appended claims.

What we claim is:

l. A method of geophysical prospecting of ore deposits comprising connecting a source of current to an ore body; passing an electric current of gradually changing intensity through said ore body; thereby exciting on the boundary of said ore body with enclosing rocks successive electrochemical reactions following one another as the intensity of the current is changed each of said reactions having a definite specific electrochemical potentialand a limit current intensity; simultaneously registering the potential values of the ore body relative to the enclosing rocks and the values of said exciting current, discriminating the value of said electrochemical potential at the boundary of said ore body withsaid enclosing rocks from said registered potential value by excluding an ohmic drop of potential in the section of the exciting current path incorporating the enclosing rocks where said potential is registered; subtracting from the value of said potential, measured for every value of current intensity, a value proportional to each respective value of the current intensity; selecting a proportionality factor for each cycle of the current'being passed, said proportionality factor being equal to the smallest value of the ratio of the registered potential increment to the increment of said exciting current causing said potential increment; developing, from the thus obtained value of the electrochemical potential, curves of the dependence of the value of said electrochemical potential on the boundary of said ore body with said enparing thereafter the values of said specific potential with tabular values adjusted by a proportionality factor of the sum of limit currents to the size of the entire ore body surface and thereby determining the mineral composition and size of the ore body.

2. A method of geophysical prospecting of ore deposits comprising connecting a source of current to enclosing rocks; passing an electrical current of gradually varying intensity through the ore body without direct contact of said source of current with said ore body; exciting successive electrochemical' reactions on the boundary of said ore body with said enclosing rocks, said reactions following one another as the intensity of the current is changed; each of said reactions having a definite specific electrochemical potential and limit current intensity, simultaneously registering apparent potential values of the ore body relative to the enclosing rocks and the value of said exciting current; discriminating the value of said apparent electrochemical potential from the value of said registered apparent potential by excluding an ohmic drop of potential in the section of the exciting current flow path where said apparent potential is registered, subtracting from said value of apparent potential, measured for every value of current intensity, a value proportional to each respective value of current intensity; selecting a proportionality factor for each cycle of the current being passed, said proportionality factor being equal to the smallest value of the ratio of the increment of said registered apparent potential to said exciting current intensity increment, causing said registered apparent potential increment; developing from the thus obtained values of said apparent potential, electrochemical curves of the dependence of the value of said apparent electrochemical potential upon the exciting current intensity value; establishing from said dependence curves specific apparent potential values and the value of said limit current intensity for each electrochemical reaction utilizing known relationships relating the distribution of the potential in the periphery of the ore body with its position, size and shape and the values of the potential on the boundary of the ore body, determining with the help of said relationships the specific true potential on the boundary of the ore body with said enclosing rocks and also the position, size and shape of said ore body, comparing said spedific true potential values with tabular values and thereby establishing the mineral compositionof said ore bodies. 

1. A method of geophysical prospecting of ore deposits comprising connecting a source of current to an ore body; passing an electric current of gradually changing intensity through said ore body; thereby exciting on the boundary of said ore body with enclosing rocks successive electrochemical reactions following one another as the intensity of the cuRrent is changed each of said reactions having a definite specific electrochemical potential and a limit current intensity; simultaneously registering the potential values of the ore body relative to the enclosing rocks and the values of said exciting current, discriminating the value of said electrochemical potential at the boundary of said ore body with said enclosing rocks from said registered potential value by excluding an ohmic drop of potential in the section of the exciting current path incorporating the enclosing rocks where said potential is registered; subtracting from the value of said potential, measured for every value of current intensity, a value proportional to each respective value of the current intensity; selecting a proportionality factor for each cycle of the current being passed, said proportionality factor being equal to the smallest value of the ratio of the registered potential increment to the increment of said exciting current causing said potential increment; developing, from the thus obtained value of the electrochemical potential, curves of the dependence of the value of said electrochemical potential on the boundary of said ore body with said enclosing rocks upon the exciting current intensity value, establishing from said curves of dependence the values of said specific potential and the value of said limit current intensity for each electrochemical reaction; comparing thereafter the values of said specific potential with tabular values adjusted by a proportionality factor of the sum of limit currents to the size of the entire ore body surface and thereby determining the mineral composition and size of the ore body.
 2. A method of geophysical prospecting of ore deposits comprising connecting a source of current to enclosing rocks; passing an electrical current of gradually varying intensity through the ore body without direct contact of said source of current with said ore body; exciting successive electrochemical reactions on the boundary of said ore body with said enclosing rocks, said reactions following one another as the intensity of the current is changed; each of said reactions having a definite specific electrochemical potential and limit current intensity, simultaneously registering apparent potential values of the ore body relative to the enclosing rocks and the value of said exciting current; discriminating the value of said apparent electrochemical potential from the value of said registered apparent potential by excluding an ohmic drop of potential in the section of the exciting current flow path where said apparent potential is registered, subtracting from said value of apparent potential, measured for every value of current intensity, a value proportional to each respective value of current intensity; selecting a proportionality factor for each cycle of the current being passed, said proportionality factor being equal to the smallest value of the ratio of the increment of said registered apparent potential to said exciting current intensity increment, causing said registered apparent potential increment; developing from the thus obtained values of said apparent potential, electrochemical curves of the dependence of the value of said apparent electrochemical potential upon the exciting current intensity value; establishing from said dependence curves specific apparent potential values and the value of said limit current intensity for each electrochemical reaction utilizing known relationships relating the distribution of the potential in the periphery of the ore body with its position, size and shape and the values of the potential on the boundary of the ore body, determining with the help of said relationships the specific true potential on the boundary of the ore body with said enclosing rocks and also the position, size and shape of said ore body, comparing said spedific true potential values with tabular values and thereby establishing the mineral composition of said ore bodies. 